Tumor cells often retain the capacity for differentiation and maturation into non-replicating terminal cells. The purpose of this project is to characterize the sequence of changes which occur in malignant melanocytes as they differentiate, mature, and die, and to explore the possibility that the rate at which this process occurs is a function of an intrinsic cyclic nucleotide dependent, intracellular regulatory mechanism. By increasing the rate at which tumor cells differentiate, mature, and die, tumor growth may be retarded or stopped completely.